The plural of tomato is tomatoes, ending in oes, and like most spelling rules, the reason it's done is because that's the way it's always been done. There are a few guidelin…es for when to add ES to words that end in O, but the simplest way to handle the problem is just to memorize a list of common words that do it: buffalo buffaloes domino dominoes echo echoes embargo embargoes hero heroes mosquito mosquitoes potato potatoes tomato tomatoes torpedo torpedoes veto vetoes Otherwise you can usually just add an S.

Some nouns ending with an 'o' preceded by a consonant add 'es' to the end of the word to form the plural; for example: tomato - tomatoes potato - potatoes hero …- heroes echo - echoes buffalo - buffaloes mosquito - mosquitoes Most nouns ending with an 'o' simply add 's' to the end of the word to form the plural; for example: zero - zeros zoo - zoos studio - studios radio - radios avacado - avacados auto - autos